Asthma is an increasingly important health concern. The prevalence of asthma increased 100 percent worldwide between 1985 and 2001, and deaths from asthma are rising. About 300 million people have asthma.

The study analyzed birth data from more than 95,000 children and their mothers in Tennessee. Having bronchitis during infancy was associated with an increased risk of childhood asthma. And for children born in the fall, the risk was the greatest. Those children have a nearly 30 percent increased risk of developing asthma.

Researchers believe the relationship is due both to genetic causes that predispose some people to developing asthma, and exposure to winter viral infections at a young age.